1. Field of the Invention
The present invention relates to a method of forming a metal film and, more particularly, to a method of forming an Al deposition film preferably applied to a wiring layer in a semiconductor integrated circuit device or the like.
2. Related Background Art
Aluminum (Al), Al--Si, and the like have been mainly used as materials for electrodes and wiring layers in conventional electronic devices and integrated circuits using semiconductors. Since Al is inexpensive, has a high electrical conductivity, and can form a dense oxide film on a surface, an internal structure can be chemically protected and stabilized by an Al deposition layer. In addition, Al has a high adhesion strength with Si, thus providing various advantages.
In recent years, since the packing density of integrated circuits such as LSIs has been increased and micropatterning of wiring layers and formation of multi-layered wiring films have been required, more strict conditions are imposed on conventional Al wiring layers. Along with an increase in density of micropatterning as a result of an increase of the packing density, surfaces of LSIs and the like have been roughened due to oxidation, diffusion, thin-film deposition, etching, and the like. For example, an electrode and a wiring metal must have excellent step coverage without any disconnection when they are deposited on stepped surfaces. At the same time, the electrode and the wiring metal must be deposited in small, deep via holes. In a 4- or 16-Mbit DRAM (dynamic RAM), an aspect ratio (i.e., (length of via hole).div.(diameter of via hole)) of a via hole in which a metal such as Al must be deposited is 1.0 or more. The diameter of the via hole itself becomes 1 .mu.m or less. Therefore, a technique for depositing Al in a via hole having a high aspect ratio is required.
Al or the like must be deposited not only in the via hole but also on an insulating film. In addition, this deposition film must be excellent in quality.
The present inventors have recently proposed a CVD method using a dimethylaluminum hydride as a technique for forming an Al film.
This method is effective as a future micropatterning technique in semiconductor fabrication techniques. However, there is much left to be solved to increase a production yield of semiconductor devices, decrease the cost, and achieve an industrial success in the following respects.
There is a method of forming a flat multi-layered wiring pattern, including the step of forming an insulating film having a square contact hole having a side of 0.8 .mu.m in a monocrystalline silicon substrate and selectively depositing monocrystalline aluminum in this contact hole by a CVD method using DMAH and hydrogen, the step of forming an electrode extraction layer consisting of a conductive material (e.g., W or titanium nitride) on the aluminum and the insulating layer, and the step of depositing aluminum on the entire surface. When this method is used, aluminum can be selectively deposited in the contact hole with good reproducibility. However, aluminum on titanium nitride is not deposited with good reproducibility as in aluminum deposited in the contact hole.
When a barrier metal such as titanium nitride is formed in a contact hole and aluminum is to be selectively deposited thereon, reproducibility is often degraded as compared with aluminum directly deposited on monocrystalline silicon.
When annealing is repeatedly performed in the semiconductor fabrication process, disconnections and short circuits may be formed in wiring layers. This typically occurs in a wiring film having three or more layers.
The present inventors have made various experiments and extensive studies to find a reason for reduction of a product yield because the following causes interaction with each other.
The first cause is formation of defects during initial aluminum deposition. The second cause is a problem of an interface between aluminum and an underlying material when aluminum is deposited in a contact hole defined by the underlying material. The third cause is a migration problem. Another cause is a difference in yield between aluminum deposited in the contact hole and aluminum formed on the underlying layer, i.e., the insulating film during formation and a difference in film quality therebetween.